The Metasploit project, has released a tool that demonstrate a system for identifying the real IP address of a web user, regardless of proxy settings, using a combination of client-side technologies and custom services. No vulnerabilities are exploited by this tool. A properly configured Tor setup should not result in any identifying information being exposed.

It's an interesting tool, to check if your proxy configuration is really anonymizing your connections, or if you are under a false anonymity.